1. Field of the Invention
The present invention relates to an expansion network for increasing the number of subscriber terminations at a passive optical bus system comprising optical mixers, for example, what referred to as star couplers.
2. Description of the Prior Art
Passive optical mixers, so-called star couplers, which are useable for the formation of an optical bus system have limited number of inputs and outputs. When one wishes to connect more subscribers, for example, sub-task computers in a multicomputer system, to the bus system, then a plurality of star couplers must be interconnected in a suitable manner to form a system.
One possibility for expanding coupler networks to be formed in such a manner is known from the German published application No. 31 23 445, fully incorporated herein by this reference This known expansion possibility has the advantage that opto-electrical amplifiers can be inserted into he appertaining, required light conductors between the star couplers with little expense, the opto-electric amplifiers regenerating the light signals and reducing the attenuation in the coupler network. With respect to transit times and subscriber connection, the meshed star couplers essentially behave in the manner that a correspondingly large coupler would behave when they are joined in close spatial proximity. For ideal optical components, the transmission loss is likewise the same as given a single coupler but, in practice, a few decibels of additional losses are added due to losses in the mixer and, under given conditions, in the required, optical plugs. The signal transit times and attenuations occurring, however, can be disadvantageous, particularly in multicomputer systems.